Model systems for the study of carcinogenesis in cultured human bronchus, peripheral lung and pancreatic duct have been developed. Explants of human bronchus, peripheral lung and pancreatic duct have been maintained in culture for 6 months, 24 days and 2 months, respectively. The metabolism of several classes of chemical carcinogens have been investigated in human bronchus, and that of benzo(a)pyrene in peripheral lung and pancreatic duct. Human bronchial epithelial cells have been grown in culture for periods of 8-10 months. Immunofluorescence and immunoperoxidase methods are being employed for the identification of both normal and carcinogen-transformed bronchial epithelial cells in tissue specimens and in cell cultures. Normal-appearing explants of human bronchus and pancreatic duct have been exposed to carcinogens. Examination of the carcinogen-treated explants by light and electron microscopy revealed marked cellular atypia in the epithelium. In addition, autoradiograms showed an increase in the labeling index of carcinogen-treated tissues with 3H-thymidine. The tumorigenic potential of these carcinogen-induced lesions is being assessed in athymic nude mice.